LISBON (Reuters) - Portugal's Constitutional Court on Friday upheld a ban on same-sex marriages, just two months before a general election in which the ruling Socialist Party is campaigning to allow such unions.

The court said in a statement it had reviewed a successful appeal by two women, Teresa Pires and Helena Paixao, against an earlier court ruling, which had denied them the right to wed, and reverted to the lower court's verdict by three votes to two.

The women were first denied the right to marry in a civil registry office in 2006 and have since been trying to overturn the decision using an article of the constitution which bans discrimination based on sexual orientation.

"The decision makes more evident the urgency of solving this issue via parliament by parties wanting to fight discrimination and promote basic equality," the Portuguese chapter of the International Gay and Lesbian Association said in a statement.

It said it was important that the court's decision was not unanimous and cited growing social and political support of its cause, expecting changes to occur in parliament soon.

On Wednesday, Prime Minister Jose Socrates and his Socialist Party presented its manifesto for the Sept. 27 general election. Allowing people of the same sex to wed in the predominantly Roman Catholic country was among the proposals.

Opinion polls show the ruling party virtually even with the opposition Social Democrats.

The latest poll by published on Friday by SIC/Expresso/Radio Renascenca showed the Socialists with 33 percent of voting intentions and the Social Democrats with 31.1 percent. Undecided voters made up 22.8 percent.

Gay marriage is allowed in neighbouring Spain as well as in Belgium, the Netherlands, Norway, Sweden, South Africa, Canada and some U.S. states.

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